This invention relates solenoid valves, and more particularly to fast response fluid flow control solenoid valves.
Previously, in order to position and control an actuating piston, it was necessary to control the flow into and out of the piston by an expensive electrohydraulic servo valve, and the pressure was increased in an analog manner. The new approach is to control pressure with inexpensive fast response on-off solenoid valves. These valves provide finite control as the solenoids are milliseconds fast. A small computer varies the amount of on-time and off-time so that the average fluid flow through the solenoid is smoothly variable.
In the design of such high-speed solenoid valves, it is essential that any lubricant employed in the magnetic radial gap have a boundary with minimum thickness and be uniform in thickness, since its presence defines a non-magnetic barrier. Non-uniformity causes differences in operating speeds, and hence fluctuations in the resulting flow (pressure) curves required. In essence the lubricant can contribute to the non-linearity of the valve because of different operating and release times.
It is also imperative that any products shed from the lubricant be non-contaminative, since orifices, seats, and controls of, for example, pneumatic missile systems are very tiny and sensitive to contamination. Attempts have been made with various materials to satisfy these requirements, including combinations of soft and hard platings, dry-film lubricants, such as teflon and molybdenum disulphide derivatives and mechanical hard surfacing techniques. The results were unsatisfactory, none meeting the required combination of consistency, non-contaminatory, and long life. For example, the thickness of the plating combinations were variable, and even though specified closely varied from lot to lot in all combinations. Further, the materials lasted for far too short a time, or resulted in unacceptable debris either from the plating or lubricant, or the base material became galled and fretted.
In order to overcome the foregoing problems and deficiencies of the prior art, an improved high-speed solenoid valve is hereinafter described.